Current practice for NOx tuning of gas combustor turbines, used in power plants for example, is to make incremental adjustments until a target NOx emissions level is achieved. This process can be time consuming and requires a technician to interrupt the normal operation of the gas turbine.
Gas turbines, typically have multiple combustion chambers. The combustion chambers are termed “cans” in the art. The can to can variation in terms of fuel to air ratio leads to some cans being hotter, i.e. higher flame (or firing) temperature than others due to higher fuel to air ratio than other cans. These cans exhibit higher Nitrogen Oxides (NOx) emissions and certain pressure dynamic spectral tones corresponding to higher flame temperature tend to be stronger. On the other hand, this variation can lead to one can burning very lean or almost “blowing out” (i.e., flame extinguishes), if for example, the fuel to air ratio is below a certain threshold. The blowout of a combustion chamber or a can is termed “Lean Blow out” or LBO. Colder cans have higher LBO risk and higher Carbon Monoxide (CO) emissions due to leaner fuel to air ratio than hotter cans that have higher NOx emissions due to higher fuel to air ratio. Colder cans also have certain dynamic tones that respond to colder firing temperature, i.e., tones that increase in amplitude as firing temperature decreases
Using pressure vibration sensors, feedback for each can, fuel flow and airflow is scheduled at the global or turbine level (total air and fuel for all the cans) to meet turbine load requirements such that the combustion dynamics in each can and emissions at the turbine level are within acceptable limits. Specifically, according to current combustion tuning practice, the overall fuel splits from the fuel system to the cans and the bulk fuel flow are set through the main fuel gas control valves.
However, an efficient method for tuning the f/a ratio in relation to NOx emissions is needed to ensure uniform life of the cans and to provide more efficient operation of the turbine and reduced emissions.
Thus, for example, in regard to NOx emissions a system that enables adjustment of the fuel to air ratio of individual fuel valves in order to meet defined NOx emission targets is needed.